A commercially available 99mTc-generator is an instrument for extracting the metastable isotope 99mTc from a source containing decaying 99Mo, for example with the aid of solvent extraction or chromatography.
99Mo in turn is usually obtained from a method which uses highly enriched uranium 235U as a target. 99Mo is created as a fission product by irradiating the target with neutrons. However, as a result of international treaties, it will become ever more difficult in future to operate reactors with highly enriched uranium, which could lead to a bottleneck in the supply of radionuclides for SPECT imaging.
U.S. Pat. No. 5,802,438 discloses a method for producing 99mTc by irradiating a Mo-metal target in the surroundings of a reactor. HU 53668 (A3) and HU 37359 (A2) describe methods in which 99mTc is obtained with the aid of sublimation processes.